Britney Spears is happy and engaged, but her ex-husband, Jason Alexander exclusively tells Star magazine that he doesn’t see it working out.

Alexander — who married the Oops!…I Did It Again singer in January 2004 (the union was annulled after just 55 hours) — calls her relationship with fiancé Jason Trawick “a complete sham,” and claims Trawick, 40, “will end up hurting” Spears, 30.

He told Star exclusively, “If they actually get married, it will probably only last for a year two, but not much longer than that.”

Alexander told Star he feels the pop singer must have felt between a rock and a hard place when she accepted the talent agent’s marriage proposal on December 15. The engaged duo publicly celebrated their union, and Trawick’s 40th birthday, at Las Vegas’ Sugar Factory American Brasserie the next day, with the southern belle proudly sporting a three-carat Neil Lane engagement ring.

Alexander told Star that mutual friends tell him Spears feels like she’s being watched constantly, and has been averse to fight her father Jamie’s conservatorship to avoid custody issues with her sons from ex-hubby Kevin Federline.